Method and apparatus for preparing continuous webs of fibrous material



June 22, 1965 p o rz E 3,190,790

METHOD AND APPARATUS FOR PREPARING CONTINUOUS WEBS 0F FIBROUS MATERIAL Filed April 24, 1962 4 Sheets-Sheet 1 A TTOANEY June 22, 1965 -r. PLOETZ EI'AL 3,190,790

METHOD AND APPARATUS FOR PREPARING CONTINUOUS WEBS OF FIBRQUS MATERIAL Filed April 24, 1962 4 Sheets-Sheet 2 INVENTOR. THEODOR PL 0572 KLA US W/MMEI? We/3mm 3,190,790 nous June 22, 1965 T. PLOETZ ETAL METHOD AND APPARATUS FOR PREPARING CUHTIN WEBS OF FIBROUS M'IZEEIAL 4 shees sheet 3 Filed April 24, 1962 INVENJiORi T175000! PLOEFZ KwAus w/MMER R MT ATTORNEY" 3,190,790 INUOUS June 22, 1965 -r. PLCJETZ ETAL METHOD AND APPARATUS FOR PREPARING CONT WEBS OF FIBROUS MATERIAL 4 Sheets-Sheet 4 Filed April 24, 1962 INVENTOR. D0? KLAl/S km 3. m

TI /0 PLOETZ W/MMER ATTORNEY United States Patent METHOD AND APPARATUS FOR PREPARING (IQNTENUOUS WEES 0F FIERGUS MATERIAL Theodor Ploetz, Hosel, Freis Mettmann, and Kiaus Wimmer, Hillegossen, near Bielefeld, Germany, assignors to Feldmuhle Aktiengesellschaft, Dusseldorf- Uherkassel, Germany Filed Apr. 24, 1962, Ser. No. 189,778 Claims priority, application Germany, Apr. 26, 1961, F 33,764; July 14, 1961, F 34,434 13 Claims. (Cl. 162-212) This invention relates to a method of preparing continuous webs of fibrous material and to a modified paper making machine for performing the method.

Paper making machines of the Fourdrinier type employing sloping screens have previously been used to advantage when fibers of relatively great length, such as most synthetic fibers, are to be made into a continuous web. Sloping screens are preferred, for example, in the manufacture of porous paper for tea bags. The webs initially deposited on a screen from fiber suspensions do not offer much resistance to the flow of water through the screen, and the webs can be formed from heavily diluted stocks.

The known Fourdrinier type paper making machines with sloping screens have heretofore not been practical for the manufacture of relatively thick webs, or for relatively dense and impermeable thin webs. While the screen passes upward through the suspension of the fibrous material in the known apparatus, the fibers are deposited on the wire, and a sheet is formed. In the lower portion of the sheet forming Zone, the sheet consists of individual fibers which are predominantly spaced from each other. The sheet is thin, irregular, and lacks continuity. Water is drawn off freely.

As the screen continues traveling through the suspension, a heavier mat is formed which resists the passage of the aqueous phase of the suspension. The flow of stock ahead of the densely coated screen is slower, and the amount of water passed through the screen is smaller than in the lower portions of the screen. The fiow pattern immediately adjacent the higher portions of the sloping screen in known apparatus is more turbulent than in the lower portions, and there is liquid movement in a downward direction. The turbulence is not readily controlled. Partial removal of the previously deposited fibrous material from the mat and non-uniformity of the web are practically unavoidable.

A suction box arranged adjacent the back face of the screen can increase the overall pressure ditference between the two screen faces, and thereby increases the rate of Water removal, but the negative pressure uniformly distributed about the entire box orifice adjacent the screen cannot equalize the flow rate and cannot change the resulting unfavorable flow pattern.

It has heretofore been necessary to combine the webs from several fiat screens or from fiat and cylinder screens when heavy or dense fiber webs were to be prepared from' suspensions of fibrous particles. Several thin webs pre pared on separate screens are combined on a couch press while wet. There cannot be much interweaving of fibers between the several layers united in this manner, and such composite webs tend to split into the constituent layers. The manufacturing method is relatively complicated and the apparatus required is costly to build and to operate.

The object of this invention is a method of preparing heavy webs of fibrous materials which is simple and capable of being performed on a single paper-making machine of the Fourdrinier type.

Another object is a method in which a plurality of layers of fibrous material is produced in a single operation and interwoven to prevent separation of the several layers.

A more specific object is the preparation of multi-ply paper-like products in a single operation and on a single piece of machinery.

A further object is the provision of apparatus for carrying out the method of the invention in the several aspects thereof.

Other objects and manyof the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: a

FIG. 1 shows a paper making machine of the invention in fragmentary sectional side elevation on the line II of FIG. 2;

FIG. 2 shows the apparatus of FIG. 1 in planview and partly in section on the line II-II;

FIG. 3 illustrates a modified apparatus of the invention in a fragmentary side elevational view taken on the line IIIIH of FIG. 4;

FIG. 4 shows the apparatus of FIG. 3 in on the line IV-IV;

FIG. 5 illustrates a further modification of the apparatus of FIG. 3 in a corresponding view;

FIG. 6 shows the device of FIG. 5 in plan view, partially in section on the line VIVI;

FIG. 7 shows a detail of FIG. 5 on an enlarged scale; and a a FIG. 8 diagrammatically illustrates the mode of operation of the several embodiments of the invention, and more particularly of those shown in FIGS. 3 to 7.

Referring firstly to FIGS. 1 and 2, there is shown a feed box 1 which is of generally rectangular elongated shape and open at the top. An inlet conduit 2 connects one end portion of the box 1 with a mixing chest in a manner not further illustrated in FIGS. 1 and 2. A non illustrated pump in the conduit 2 maintains in the box 1 a suspension 1'3 of fibrous material in an aqueous liquid at a substantially constant level. Four bafile plates 3 plan section are horizontally arranged in the central portion of the box 1 and are vertically spaced from each other below the surface of the suspension 13.

The lower part of the other longitudinal end portion of the box .1 is cut away in an oblique plane, and the resulting opening is covered by an upwardly sloping portion of a Fourdrinier screen 4 which is roller driven in the usual manner and travels in the direction of the arrow 14. The screen 4 has been partly omitted from FIG. 2 so as to reveal other portions of the apparatus.

A liquid filled vat 10 is joined to the box 1 and encloses the portion of the screen 4 which approaches the box 1. Five fiat vacuum chests 6 are superimposed upon each other in the vat it Each chest is as wide as the screen 4 and approximately as long in a horizontal plane as it is wide. The combined height of the chests is similar to the immersed depth of the straight sloping portion of the screen 4. The chests are staggered'longitudinally at an angle corresponding to the slope of the adjacent portion of the screen 4. The chambers 6 are open toward the screen and their open ends are beveled in a common plane so as to provide a support for the sloping screen portion which substantially seals the orifices of the chambers.

A system of manifolds 15 and discharge pipes 12 connects the end of each vacuum chest 6 to a suction pun-1pv ally conventional, and have been indicated in a conventional manner. Idler rolls 11 and 7 at the bottom and top respectively of the sloping portion of the screen 4- guide the same into a path over the beveled end portions of the chests 6 in sealing engagement with the box 1. The screen 4 is guided from the idler roll 7 over four table rolls 8 of conventional type, and over two suction boxes 9. Much of the residual water is removed from the fiber web which forms on the sloping screen portion on the table rolls 8 and by the suction boxes 9. A return roll 17 at the dry end of the screen 4 is motor driven in a conventional manner.

It will be understood that means are provided to tension the screen. Such tensioning means, lateral seals, and other well-known devices not directly relevant to this invention have been omitted from the drawing, and do not require further description.

The apparatus illustrated in FIGS. 1 and 2 operates in the following manner:

A suspension of fibrous material in an aqueous carrier is pumped through the conduit 2 into the box 1. The direction of flow in the conduit 2 is vertically upward, but flow in the box 1 is predominantly horizontal, and horizontal movement is guided by the parallel baffle plates 3. The transition from vertical to horizontal flow near the orifice of the conduit 2 in the longitudinal end portion of the box 1 causes intense turbulence. The fibers which may have assumed a preferred parallel orientation in the direction of fiow through the conduit 2 are oriented at random when they enter the flat passages between the battle plates 3.

In these passages, the flow of the stock becomes increasingly linear, but the passage length is selected in such a manner that parallel orientation of the fibers is avoided. It is entirely feasible to have the stock emerge in substantially linear fluid flow from the passage between the baffle plates 3. Some turbulence is again generated as the streaming liquid passes the trailing edges of the baffle plates 3, that is, the edges spaccdly opposite the moving screen 4, but spacing the trailing edges of the battles at a small distance from the screen permits the turbulence to be attenuated to an insignificant magnitude before the suspension meets the screen 4. If stock of greatly varying consistency and fiow properties is to be handled in the same machine, the baffles 3 are preferably made removable and adjustable so that bafile plates may be arranged at different distances from each other, from the face of the screen 4, and from the conduit 2. The battles are preferably arranged in common horizontal planes with the walls which separate adjacent vacuum chests 6.

The valves in the discharge lines 12 are set in such a manner that the pressure differential between the two faces of the screen 4 increases in the direction of screen movement. As a fiber web builds up on the screen, it passes over the orifices of successive chambers 6 in which the negative pressure increases in accordance with the increasing flow resistance of the fiber web. Proper control of vacuum in the chests 6 permits a uniform rate of water discharge from each chamber to be established. The chambers are of uniform height and of uniform orifice size. The uniform discharge of liquid from the pipes 12 thus causes uniform flow of stock on the feed box 1 toward the screen 4 over the entire cross section of the box 1. Straight linear flow is maintained from a point between the baffie plates 3 to the upstream face of the screen 4.

The vacuum chests 6 are elongated in the direction of fluid flow in the box 1 in the vertical section plane of FIG. 1, and there is no change in the direction of flow as the aqueous liquid substantially separated from the fibrous material emerges from the downstream face of the screen and proceeds through the chambers 6. We have found that lack of turbulence ahead of the screen 4 depends to a very substantial extent on maintaining the same direction of liquid flow toward one screen face and away from the other screen face. Turbulence in the critical area immediately ahead of the upstream screen face is virtually eliminated, and the fibers are deposited in the random orientation resulting from the turbulence at the orifice of the conduit 2'. The mechanical properties of the web, and of the final product made from the web are uniform in the direction of machine movement and at right angles thereto, and the strength of the product is greatly increased.

The velocity of the fiber suspension approaching the screen is approximately equal to the velocity of screen movement in conventional paper making machinery employing a sloping screen. We have found that a portion of the approaching liquid is carried along by friction with the screen face under such conditions, and that a significant amount of turbulence is generated thereby to unfavorably affect the properties of the web. The improved rate of liquid withdrawal obtained in the modified apparatus of this invention makes it feasible to increase the flow velocity of the fiber suspension to a multiple of the screen speed.

The velocity of liquid flow toward the screen should be at least twice the velocity of screen movement, and it is preferable to pass the liquid through the screen at even higher rates. A flow velocity five times the screen velocity has been found to be entirely practical, and higher flow velocities are undoubtedly feasible with suction pumps of sufiicient capacity. The uniformity of the sheet formed on the screen and the interweaving of its fibers increase significantly with the velocity of the liquid flow. This is believed to be largely due to reduced turbulence adjacent the upstream face of the screen, and to better retention of the web particles by the rapidly moving liquid.

The slope or pitch of the screen may be chosen freely at high flow velocities since the effects of gravity become relatively unimportant. With a fluid flow of twice to five times the screen velocity, and a stock consistency of the order of magnitude of 0.1 to 0.3 percent, the slope of the screen is preferably between 20 and 60 degrees, and the common direction of liquid flow in the approach channel constituted by the box 1, and in the discharge channel constituted by the several vacuum chests 6 is preferably horizontal, or has at least a predominant horizontal component.

The useful length of the sheet forming zone on the screen 4, that is, the useful depth of immersion of the screen in the box 1, is largely determined by the capacity of the suction pumps connected to the vacuum chests 6, and is greater than with a single vacuum box under otherwise equal conditions. The apparatus illustrated in FfGS. 1 and 2 may therefore be operated at higher screen speeds than otherwise similar machinery not having a plurality of independent vacuum chests to produce webs of equal weight, or at the same speed to produce heavier webs. It is also feasible to operate with stock of very low consistency which favors homogeneity of the web produced even at high screen speeds.

The apparatus illustrated in FIGS. 1 and 2 permits the production of relatively heavy webs not attainable with conventional equipment in a single step. When the apparatus is employed for making light webs, water sheets produced from greatly diluted stocks have exceptional translucency, uniformity, and density.

The ability of the apparatus of handling large amounts of liquid in stock of low consistency is particularly advantageous in the preparation of webs from long-fibered material such as most synthetic materials currently employed in the making of paper and paper-like products. With a plurality of vacuum chests controlled for uniform liquid flow across the upstream face of the screen, it is not necessary to shake the screen for improved sheet transparency and better mechanical properties. Elimination of the shaking mechanism simplifies the operation of the machinery, and reduces its bulk and cost. Another advantage of the apparatus of the invention is its flexibility. While conventional paper making ma chinery operates at highest efiiciency only within a narrow range of operating conditions, the apparatus of the invention can be readily and simply adjusted to handle suspensions of fibrous particles which differ greatly in their characteristics. Paper may be made from cellulose, from synthetic fibers, and from mixtures of both on the same machine at peak production rates without compromising the quality of the product.

When the bafiie plates 3 in the apparatus of FIGS. 1 and 2 are moved close enough to the screen 4 to make the intervening gap merely as wide as the deposited web is thick, the passages between the baffle plates constitute individual and separate inlet channels which may be connected to individual supplies of different suspensions to form a multi-ply web on the sloping screen.

FIGS. 3 and 4 illustrate an embodiment of the invention modified for making a three-ply web of fibrous material in which the several plies may be of different materials, yet are firmly interwoven at the interfaces.

The three-ply web is formed on a sloping portion of a screen 4 the wet end of which is partially enclosed in a vat lit. The portion of the apparatus downstream from the screen 4 is substantially identical with the corresponding portion of the apparatus shown in FIGS. 1 and 2 and includes five vacuum chests 6a to de superimposed to support the sloping portion of the screen 4 on their orifices 16a to 16s. The chests guide the liquid passed through the screen in five straight horizontal.

streams to discharge pipes 12.

The feed box 1a is subdivided by partition walls 3a, 3b into three horizontal approach channels 18a, 18b, and 18c connected to respective supplies of fiber suspensions by vertical conduits 2a, 2b, 2c. The lowermost approach channel 18:: is horizontally aligned with the lowermost vacuum chest 61:, the height of the intermediate channel 18b is equal to the combined height of the vacuum chests 6b and dc with which the channel 18b is aligned, and the uppermost channel 180 which is open to the atmosphere cooperates with the two topmost vacuum chests 6d and 6e.

The fibers in the several suspensions separately fed to the approach channels 18a, 18b, The through the vertical conduits 2a, 2b, 2c are oriented at random by the transition from vertical to horizontal flow as they enter the approach channels, and the resulting turbulence in the liquid is attenuated by the horizontal flow until it becomes insignificant. It will be understood that horizontal baffie plates may be arranged within each approach channel in a manner evident from FIG. 1, and the positions of the bafiie plates may be variable as described hereinabove. The horizontal spacing of the partition walls 3a, 31) from the screen 4 may also be adjusted if desired by telescoping the two portions of each partition wall shown in FIG. 3;

The white water withdrawn from the screen 4 through the several discharge pipes 12 is handled separately for vacuum chests cooperating with approach channels feeding diiferent suspensions. The white water still contains fibers shorter than the size of the apertures in the screen 4, or fibers oriented in the direction of liquid flow when approaching the screen 4. To salvage such fibers, and

j to reduce the amount of stream polluting waste water from the operating of the machine, the white water is employed for making up additional amounts of the corresponding suspensions by mixing the liquid with additional amounts of fibrous material in a manner that will be more fully described hereinafter.

An outside layer of a web is formed at the orifice 16a of the lowermost vacuum chest (in from fibers of a suspension fed from the approach channel 18a. The rate at which this outside layer is deposited may be controlled by selecting the consistency of the suspension, and by varying the rate of How of the suspension relative to the speed of the screen 4. The flow rate may be regulated by adjusting the negative pressure in the chest 611, by,

varying the pressure at which the suspension is pumped into the approach channel 18a, or by both. The pressure difference between the liquids adjacent the two faces of the screen 4 is the controlling factor.

Escape of fiber suspension from the channel 18a along the screen 4 in a direction opposite to the direction of screen movement is largely avoided by filling the vat it) with Water to a level 19 sufiicient to approximately balance the positive pressure in the channel 18a. This level may be controlled by non-illustrated known devices sensitive to the pressure in the channel 13a and in the vat 19 adjacent the chest 6a to open and close solenoid actuated water supply and drainvalves when the sensed pressures differ. The apparatus illustrated in FIGS. 1 and 2 may be similarly equipped.

Escape of fiber suspension from the channel 18a in the direction of movement of the screen 4 may be reduced to an insignificant amount by reducing the clearance between the partition wall 1% and the surface of the web formed over the orifice 16a, and by balancing the pressures in the channels 18a and 1312. It is usually desirable to have a very small amount of the suspension from channel 18a bleed into the channel 18b for further improved interweaving of the several layers of the web formed, but movement of liquid transversely of the main stream must be held to a minimum in order to avoid turbulence. The desired limited cross flow is readily adjusted by setting control valves in the conduits 2a, 2b, and by shifting the partition wall 31) toward or away from the face of the screen 4.

The greater height of the approach channel 18b as compared to the channel 18a permits a core of greater thickness to be deposited on the outside layer it the consistencies of the suspensions in channels 18a, 18b are equal, and the suspensions flow at the same velocity, and other possible combinations of process variables will readily suggest themselves to those skilled in the art.

The topmost approach channel 13c is upwardly open, and therefore under atmospheric pressure. The pressure differential across the portion of the screen 4- on the orifice 16d may thus be varied by controlling the negative pressure in the vacuum chest 6d, and by varying the level of liquid in the channel 130. The open top of the channel permits escape of entrained gases, and also permits air to be drawn through the web on the screen into the vacuum chest 6e if this is desired.

The cooperation of two vacuum chests with each of the approach channels 18b, the permits the flow of the respective suspensions toward the upstream face of the screen 4 to be held uniform and substantially linear over the entire cross section of the channel. Obviously, more than two vacuum chests may be associated with each approach' channel, and more than one approach channel may be associated with a single corresponding vacuum chest in the manner of channel 13a when the web formed is readily permeable to the liquid phase of the suspension.

The successive layers of the web formed on the screen 4 are firmly interwoven by the suction applied, and the force required to separate the layers from each other is as great as that needed for splitting an individual layer in a plane parallel to a face of the web. While the produc identical outside layers may be prepared by deposition of fibrous material on a screen t which is guided in a sloping path by two guide rolls 7 and 11'.

A closed feed box 1b is divided by a partition wall into three superimposed horizontal approach channels 25, 26, 27. The channels 25 and 2'7 communicate with a single inlet conduit 22 which supplies the same suspension to both channels in a vertically upward stream. A vertically downward stream of another fiber suspension is fed through another inlet conduit 23 into that longitudinal end portion or" the channel in which is remote from the screen 4. No bafile plates have been shown within each approach channel, but such plates may be resorted to if the suspensions need to be guided for eliminating turbulence adjacent the screen 4.

Each approach channel 25, 26, 27 cooperates ith a respective vacuum chest 2h, 30, 31 with which it is horizontally aligned. The channels 25, 26, 27 are of different height, and the chests 29, 30, 31 similarly differ in height. To provide the desired rate of liquid discharge from the relatively high vacuum chests 30 and 31, these chests are each equipped with two manifold systems 15 and corresponding sets of discharge pipes 12.

The rate of fiber deposition in the three fiber forming zones along the sloping portion of the screen 4 may be controlled by varying the pressure at which suspensions are pumped into the conduits 22, 23, and by individually varying the negative pressure in the vacuum chests 2?, 3t, 31. Although the approach channels 25, 27 communicate, the rate of suspension flow in these channels may be individually controlled by adjustment of the vacuum in the chests 29 and 31.

in the apparatus illustrated in FIGS. 5 and 6, a vat enclosing the wet end of the screen 4 is not required. Leakage of fiber suspension from the guiding conduit 27 along the screen 4 in a direction opposite to the direction of screen movement is avoided by the provision of a resilient seal 20. This seal is shown in more detail in FIG. 7. A lip of rubber is partly recessed in an edge portion of the box lb adjacent the screen 4. The lip is flush with the surface of the box lb in the channel 27 to avoid turbulence near the upstream face f the screen 4, and resiliently abuts against the screen. Because of the oblique inclination of the screen to the approach channel, the liquid pressure in the channel 27, which is higher than atmospheric pressure, urges the lip 21 into sealing engagement with the screen 4.

The manner in which the several negative and positive pressures in the devices of the invention are controlled, and the circulation of liquid through the paper making machine and auxiliary equipment are illustrated in FIG. 8 in a fiow sheet in which the several pieces of equipment shown are represented in a conventional manner. The fiow sheet partly illustrates a paper making apparatus of the type shown in FIGS. 5 to 7, but it will be understood that the embodiments of the invention illustrated in FIGS. 1 to 4 are equipped with pumps, valves, storage and mixing tanks, and other auxiliary equipment in an analogous manner.

Referring now to H6. 8, there is seen the sloping portion of a screen 4 arranged between three superimposed approach channels 45, 46, 47, and three coordinated superimposed vacuum chests 49, 50, 51. Two different fiber suspensions are respectively fed to the channels 45, 47 from a common inlet conduit 42, and to the central channel 46 from another inlet conduit 43 in the direction of the arrows.

The vacuum chests 49, 50, 51 are connected to the inlets of respective suction pumps 52, 53, 54 through pipes which are each equipped with a pressure gauge 61 and a control valve 62 interposed between the gauge 61 and the inlet of the corresponding pump. The control valves 62 permit the vacuum in each chest 49, 50, 51 to be individually set, and may be further equipped automatically to maintain the desired vacuum in the chests in a well known manner.

The outlets of the pumps 52, 54 are connected to a common sump tank 55, and the liquid withdrawn from 8. the central vacuum chest 50 by the pump 53 is led into another sump tank 56. Both sump tanks are equipped with overflows for discharge of excess liquid to waste. The bottom of each sump tank 55, 56 is connected to the intake of a corresponding pressure pump 57, 58. Two mixing chests 59, 60 are respectively connected to the same intakes. Valves 41 in the several connecting lines permit the proportion of liquid material drawn from each mixing chest and the corresponding sump tank to be controlled. Valves 40 in the discharge lines of the pumps control the overall amount and pressure of the suspensions fed to the screen 4.

The operation of the apparatus of FIG. 8 and of such modifications of the apparatus as will be apparent from FIGS. 1 to 4 of the drawing will now be described with reference to specific examples which are illustrative of the method of the invention. It will be understood that the invention is not limited to specific materials disclosed, nor to the numerical parameters chosen.

The equipment employed in the several examples includes a screen having a width of one meter and traveling at a rate of 20 meters per minute. The screen has 35 apertures per centimeter, and it web forming section is inclined at an angle of 45 degrees unless otherwise specifically noted.

Example 1 The pump 57 feeds to the inlet conduit 42 400 liters per minute of a 0.2 percent aqueous suspension of fibrous particles prepared from spruce wood by the sulfite process. The suspension contains 3 percent rosin sizing and 5 percent kaolin as a filler, the percentages of the addition agents being calculated on the dry weight of the fibrous material. The pH of the suspension is adjusted to 4.5 by the addition of aluminum sulfate.

Simultaneously, another suspension having a consistency of 0.01 percent of fibrous material is fed by the pump 58 to the inlet conduit 43 at the rate of 12,000 liters per minute. The fibrous material is a mixture of 70 percent of stretched or drawn polyester fibers having a titer of 1.4 denier and a staple length of 6 mm., and 30 percent fibers made from the same polyester, but not stretched or drawn, and having a titer of 3 denier and a staplelength of 10 mm. The polyester is a condensation product of terephthalic acid with ethylene glycol.

The several control valves 62 are adjusted to maintain in the lowermost vacuum chest 49 a pressure differential of 10 mm. Hg, in the vacuum chest 50 of 30 mm. Hg, and in the vacuum chest 51 of 60 mm. Hg, as compared to the corresponding approach channels 47, 46, 45. The stock water drawn from the chests which still contains a small amount of fibers is permitted to stand in the sump tanks 55, 56 so that the suspended fibers may settle, and may then be drawn with a portion of the liquid into the pressure pumps 57, 58 to dilute a more concentrated stock which is made up in the mixing chests 59, 60 in the usual manner.

A web having three superimposed layers of cellulose, polyester, and cellulose fibers respectively is formed on the screen 4. The web is finished in the conventional manner by treatment on a press roll, on drying cylinders, and on a heated calender. A laminated paper having a weight of grams per square meter is obtained. The synthetic fiber core weighs 60 grams per square meter, the two outside layers of cellulose fibers each weight 20 grams per square meter, all Weights being determined under standard conditions of temperature and humidity in the usual manner.

The paper has superior dimensional stability, has no tendency to curl under the influence of humidity, and may be written or printed upon in the manner customary with papers on a cellulose basis.

The folding endurance (Schopper) is in excess of 30,000. The stretching elongation of the material when wet is only 0.05 percent when determined according to Example 2 The paper machine used in this example is equipped with two superimposed approach channels. The lower approach channel cooperates'with two vacuum chests, the upper one with a single chest.

1600 liters per minute of a 0.2 percent suspension of fibrous material are fed to the lower approach channel. The material consists of 50 percent fir sulfate pulp and 50 percent beech sulfite pulp. Simultaneously 200 liters per minute of a 0.2 percent suspension of the same pulp mixture additionally containing 3 percent rosin sizing and percent china clay, and adjusted to a pH of 4.5 are fed to the screen through the upper channel. The slope of the screen is 45 degrees. I

The pressure diiferential in the two vacuum chests cooperating with the lower approach channel is 20 and 30 mm. Hg respectively, the lower vacuum being maintained in the lower chest. The water withdrawn from both chests is combined with additional unsized pulp and recycled. The stock Water separated from the sized pulp is drawn off at a pressure differential of 50 mm. Hg and a major portion thereof is employed for diluting addit-ional sized stock.

After passing a Wet press, a drying cylinder section, and a glazing calender, the web deposited on the screen is transformed into a double layer board having a weight of 170 grams per square meter with a sized facing of .10 grams per square meter which is readily printed upon.

Example 3 A paper making machine equipped with three separate approach channels and five vacuum chests in the manner illustrated in FIGS. 3 and 4 is employed to produce a three-ply board. Reference ishad specifically to FIG. 3

500 liters per minute of a 0.3 percent suspension of a fibrous material from sorted waste paper are fed through the conduit 20 into the lowermost approach channel 1%.. 1000liters per minute of a 0.2 percent suspension of a fibrous material derived from steamed mechanical spruce pulp are fed through the conduit 2!) into the channel 18b, and 600 liters per minute of yet another suspension of fibrous material, are pumped into is the channel 180. through the conduit 20. The last mentioned suspension has a consistency of 0.1 percent, and its solid phase includes 30 percent spruce sulfite pulp, 70 percent birch sulfate pulp, together with 2 percent rosin size and 5 percent kaolin, the latter two percentage fig-..

ures being based on the dry weight of the fibrous material. The pH of the suspension is adjustedto 4.5 with aluminum sulfate.

The white water susbtantially separated from the fibers by passage through the screen 4 is withdrawn from the vacuum chest 6a at a pressure differential of 35 mm. Hg and led to a first sump tank. The vacuum chests 6b and 6c are operated respectively at pressure differentials of 4S and 60 mm. Hg and are discharged into a common second sump tank. Liquid is discharged from the vacuum chests 6d and 6e at respective pressure differentials of 70 and 75 mm. Hg, and collected in a third sump tank. The separately collected three bodies of liquid are partly recycled to combine them with the output of respective mixing tanks for diluting respective bodies of pulp.

After suitable after-treatment, the three-layer web produced yields a three-ply board having a weight of 205 grams per square meter and consisting of 100 grams per square meter of an inexpensive core of mechanical pulp, 75 grams per square meter of a better wastepaper back layer, and 30 grams per square meter of a cellulose face layer which readily accepts printing.

Example 4 Referring again to FIG. 8, 400 liters per minute of a 0.1 percent suspension of aspen sulfite pulp containing 3 percent rosin size and 4 percent titanium dioxide filler, and having a pH of 4.5 are fed through the conduit 42 to the channels 45 and 47. Simultaneously, 600 liters per minute of a 0.2 percent stock of ground and bleached pine sulfate pulp are pumped through the conduit 43 into the central channel 46. The three vacuum chests 49, 50, 51 are held at respective pressure differentials of 5, 20 and 25 mm. Hg in this order. The liquid withdrawn is partly recycled to dilute more concentrated suspensions as described above. v

When finished in the usual manner, the three-layer paper obtained has a total weight of grams per square meter. The core of high strength cellulose weighs 60 grams per square meter, and the two outside layers of sized and pigmented hard wood pulp each Weigh 10 grams per square meter.

The several layers of the paper or board products described in the examples are so firmly interwoven that they cannot be separated by any combination of heat and humidity. The mechanical properties of the laminated products in the direction of screen movement and at right angles thereto are virtually identical. The homogeneity of each layer is as good as if it had been separately formed on a screen, and combined with the other layers in a secondary operation.

The mode of operation of the apparatus illustrated in FIGS. 1 and 2 will be so obvious from the above specific examples as not to require detailed illustration. A single type of stock is fed to the conduit 2. The suspended solid phase may be the same as each of the fibrous materials referred to in Examples 1 to 4, with or without the addition of sizing, fillers, and other conventional adjuvants. Because of the uniform composition of the web portions deposited over the several orifices 16, it is not actually necessary to measure the pressure drop across each screen portion between the several vacuum chests 6 and the liquid 13 in the box 1. The valves in the discharge pipes 12 are merely set for fluid flow at equal rates from the several vacuum chests 6. The pressure gauges 61 ar ranged in each line as is evident from FIG. 8 then will automatically indicate increasing vacuum from the lowermost vacuum chests toward the topmost one.

It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the invention, andthat it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What we claim is:

1. A method of preparing a continuous web of fibrous material which comprises:

(a) moving'a continuous screen in an upward direction, said screen having two faces;

(b) separately guiding a plurality of continuous streams of suspensions of fibrous particles in a liquid in respective linear paths into simultaneous contact with respective portions of one face of said screen, said portions being olfset in said upward direction, each path extending in a predetermined direction transverse of the upward direction of movement of the associated screen portion;

(c) substantially retaining said particles of each stream on the respective face portions;

(d) passing at least a portion of the liquid in said stream through the associated screen portion from said one face to a corresponding portion of the other face of said screen; and

(e) separately guiding the passed liquid of each stream away from said portion of said other face in a linear path extending in said direction.

2. A method as set forth in claim 1, wherein said upward direction is obliquely inclined relative to said paths.

3. A method as set forth in claim 1, wherein different liquid pressure differentials between the faces of the screen portions are respectively applied to two of said screen portions for respective passage of liquid therethrough.

4. A method as set forth in claim 1, wherein each stream is guided into contact with the associated portion of said one face at a velocity which is substantially uniform over the cross section of said stream transverse of said predetermined direction.

5. A method as set forth in claim ll, wherein the velocity of each stream is substantially greater than the velocity of movement of said screen in said upward direction.

6. A method of preparing a web of fibrous material which comprises:

(a) guiding a first stream of a suspension of fibrous particles in a liquid in a straight path extending in a predetermined direction into contact with one face of a screen extending transversely of said path;

(b) substantially retaining the particles of said first stream on said one face to form a web of fibrous particles on said face;

(c) passing at least a portion of the liquid of said first stream through said screen from said one face to another face of said screen oppositie said one face;

(d) guiding the passed liquid of said first stream away from said other face in said predetermined direction;

(e) guiding a second stream of a suspension of fibrous particles in a liquid in a straight path into contact with said web on said one screen face, the path of said second stream extending in a direction transverse of said screen;

(f) substantially retaining the particles of said second stream on said fiber web;

(g) passing at least a portion of the liquid of said second stream through said web and said screen to said other face of said screen; and

(h) guiding the passed liquid of said second stream away from said other face in a straight path extending in said transverse direction.

7. A method as set forth in claim 6, wherein the paths of said first and second streams are substantially parallel.

8. In an apparatus for preparing a continuous web of fibrous material, in combination:

(a) a continuous screen having two opposite faces;

(b) drive means for moving said screen in a path extending in an upward direction;

() first guide means for separately guiding liquid fiber suspensions in linear streams to a first face of respective portions of said screen, said portions being offset in said upward direction, and said streams being transverse of said screen;

(d) pressure means for passing at least a portion of the liquid of each stream through the respective portions of said screen from said first face to the second face thereof; and

(e) second guide means for separately guiding the passed liquid of each stream away from said second face of said screen in a linear path substantially parallel to the corresponding stream.

9. In an apparatus as set forth in claim 8, said first guide means including a guide conduit, and said second guide means including a plurality of guide conduits, said conduits each being of a section elongated in a common direction in a vertical plane parallel to said upward direction, and having respective terminal portions adjacent said screen, and a bafiie plate in the guide conduit of said first guide means, said bafiie plate extending in said common direction.

10. In an apparatus as set forth in claim 8, said first and second guide means each including a plurality of guide conduits, said conduits being each of elongated section in a vertical plane parallel to said upward direction, respective conduits of said first and second guide means being associated with each of said screen portions, the conduits associated with each screen portion being elongated in a common direction, and having respective terminal portions adjacent the associated screen portion.

11. In an apparatus as set forth in claim 10, means for separately returning the passed liquid of each stream from each conduit of said second guide means to the associated conduit of said first guide means.

12. In an apparatus as set forth in claim 10, said common direction being inclined relative to said upward direction by an angle of substantially 20 to degrees.

13. In an apparatus as set forth in claim 8, said pressure means including means for maintaining a predetermined pressure differential between a suspension in said first guide means and a liquid in said second guide means.

References Cited by the Examiner UNITED STATES PATENTS 507,643 10/93 Barnes 162299 1,500,207 7/24 Shaw 1622l2 1,500,208 7/24 Shaw 162-203 1,599,385 9/26 Pryor l62320 2,134,408 10/38 Kellett 162-2l4 2,418,600 4/47 Ostertag et al 162214 DONALL H. SYLVESTER, Primary Examiner.

MORRIS O. WOLK, Examiner. 

1. A METHOD OF PREPARING A CONTINUOUS WEB OF FIBROUS MATERIAL WHICH COMPRISES: (A) MOVING A CONTINUOUS SCREEN IN AN UPWARD DIRECTION, SAID SCREEN HAVING TWO FACES; (B) SEPARATELY GUIDING A PLURALITY OF CONTINUOUS STREAMS OF SUSPENSIONS OF FIBROUS PARTICLES IN A LIQUID IN RESPECTIVE LINEAR PATHS INTO SIMULTANEOUS CONTACT WITH RESPECT PORTIONS OF ONE FACE OF SAID SCREEN, SAID PORTIONS BEING OFFSET IN SAID UPWARD DIRECTION, EACH PATH EXTENDING IN A PREDETERMINED DIRECTION TRANSVERSE OF THE UPWARD DIRECTION OF MOVEMENT OF THE ASSOCIATED SCREEN PORTION; (C) SUBSTANTIALLY RETAINING SAID PARTICLES OF EACH STREAM ON THE RESPECTIVE FACE PORTIONS; (D) PASSING AT LEAST A PORTION OF THE LIQUID IN SAID STREAM THROUGH THE ASSOCIATED SCREEN PORTION FROM SAID ONE FACE TO A CORRESPONDING PORTION OF THE OTHER FACE OF SAID SCREEN; AND (E) SEPARATELY GUIDING THE PASSED LIQUID OF EACH STREAM AWAY FROM SAID PORTION OF SAID OTHER FACE IN A LINEAR PATH EXTENDING IN SAID DIRECTION.
 8. IN AN APPARATUS FOR PREPARING A CONTINUOUS WEB OF FIBROUS MATERIAL, IN COMBINATION: (A) A CONTINUOUS SCREEN HAVING TWO OPPOSITE FACES; (B) DRIVE MEANS FOR MOVING SAID SCREEN IN A PATH EXTENDING IN AN UPWARD DIRECTION; (C) FIRST GUIDE MEANS FOR SEPARATELY GUIDING LIQUID FIBER SUSPENSIONS IN LINEAR STREAMS TO A FIRST FACE OF RESPECTIVE PORTIONS OF SAID SCREEN, SAID PORTIONS BEING OFFSET IN SAID UPWARD DIRECTION, AND SAID STREAMS BEING TRANSVERSE OF SAID SCREEN; (D) PRESSURE MEANS FOR PASING AT LEAST A PORTION OF THE LIQUID OF EACH STREAM THROUGH THE RESPECTIVE PORTIONS OF SAID SCREEN FROM SAID FIRST FACE TO THE SECOND FACE THEREOF; AND (E) SECOND GUIDE MEANS FOR SEPARATELY GUIDING THE PASSING LIQUID OF EACH STREAM AWAY FROM SAID SECOND FACE OF SAID SCREEN IN A LINEAR PATH SUBSTANTIALLY PARALLEL TO THE CORRESPONDING STREAM. 